The present invention relates generally to multiple-input multiple-output (MIMO) communications systems and, more particularly, to Tomlinson Harashima precoding with additional receiver processing in a MIMO network.
It is well known that a Generalized Decision Feedback Equalizer (GDFE) based precoder provides the optimal capacity solution for Multi-user Multiple-Input Multiple-Output (MU-MIMO) wireless systems. However, the computational cost of determining various filters associated with the GDFE precoder is often prohibitive and is not suitable for many practical systems.
There are several known precoding techniques which can enable a Base Station (BS) equipped with multiple antennas to send simultaneous data streams to multiple user terminals (UEs) in order to optimize system capacity. In general, precoding for a MU-MIMO system aims to optimize a certain criterion such as system capacity or bit error rate. Selected references are noted below, together with a description of relevant aspects of the techniques proposed therein.
C. Windpassinger, R. F. H Fischer, T. Vencel, and J. B Huber, “Precoding in multi-antenna and multi-user communications”, IEEE Transactions on Wireless Communications, pp. 1305-1316, July 2004 [1] describes a nonlinear precoding scheme known as Tomlinson-Harashima Precoding (THP). This scheme relies on successive interference pre-cancellation at the BS. A modulo operation is used to ensure that transmit power is not exceeded. Different from BD, THP triangularizes the effective channel matrix and provides somewhat higher system capacity when compared to BD. In W. Yu, “Competition and Cooperation in Multi-User Communication Environments”, PhD Dissertation, Stanford University, February 2002 [2], Wei Yu introduced the GDFE precoder and showed that it achieves a high degree of system capacity. Although, this technique achieves a high degree of system capacity, the computational cost of determining the GDFE precoder components is effectively prohibitive for a real-time implementation required by most practical systems. N. Jindal, W. Rhee, S. Vishwanath, S. A. Jafar, and A. Goldsmith, “Sum Power Iterative Water-filling for Multi-Antenna Gaussian Broadcast Channels”, IEEE Transactions on Information Theory, pp. 1570-1580, April 2005 [3] derives a very useful result referred to as the MAC/BC (multiple access channel/broadcast channel) duality. The entire disclosures of the above references are incorporated herein by reference.